PORTSMOUTH — Just half an hour before the annual St. Charles Children's Home 5K race was set to begin at Pease International Tradeport, heavy rain was coming down as runners were warming up. Soaked shoes plodded through puddles as crowds huddled underneath a large canvas tent.

But come 9 a.m., hundreds of racers emerged from their cover as the weather cleared and the 17th annual race began.

The annual 5K serves as a major fundraiser for the Children's Home, located in Rochester and celebrating its 100th anniversary this year.

Although past years and better weather conditions have welcomed larger crowds, some sisters were delighted with Monday's high turnout.

“It means a great deal to us because it shows how many volunteers we have,” said Sister Mary Rose, who ran in the race until an injury sidelined her in 2011. Now she is among a group of volunteers helping out in the tent area, where attendees ate food, registered and participated in a number of other activities.

“It's beautiful that in this rain, they still come out,” Sister Mary Rose said. “Inside people's hearts there's so much love.”

The event attracts runners from all over New England. Though there are cash prizes for early finishers, the race encourages runners of all ages and with any level of experience. Following the main race, children were encouraged to participate in a “fun run.” It is all part of what organizer and St. Charles administrator Sister Mary Agnes said is the home's largest fundraiser.

“It means a lot to us because running is part of our culture,” Sister Mary Agnes said. “We try to make it a very family-friendly event.”

She said the sisters began running with the home's children in 1996 as a way to boost self-esteem and help the staff find positive ways of interacting. According to the home's website, children at St. Charles run as much as four miles a day and five times a week. The 5K race was founded in 1997 in Rochester before moving to its current location at Pease.

Many former residents of the Children's Home return for the race each year. One 11-year-old was there with his mother and godfather. He said he looks forward to the race each year, and said St. Charles was “just a nice place.”

“It's fun,” he said. “This is my sixth time.”'

The boy's mother said the sisters were like an extended family to her son.

“I think he loves to see a lot of these people that were there for him,” she said. “They're amazing people.”

As for the race, the mom was just hoping to finish out of last place. She wasn't as worried about her son.

“He's a star,” she said.

New York City's Demesse Tefera won the race, finishing with a time of 15:32. Dover's Daniel Hocking finished second at 15:59. Nathan Huppe, also of Dover, finished in third with a time of 16:29.

On the women's side, Hirut Beyene, of New York City, won in 16:51. Heidi Westover of Walpole, N.H. finished second with a time of 17:06. Larissa Park of Sommerville, Mass. came in third at 17:16.